Impacts of Vegetation and Climate Change on Dryland Rivers: Lesssons from the Rio Puerco, New Mexico

简介：干旱的美国西部依靠河流提供大部分水资源。来自人口增长、气候变化和入侵植物物种的压力威胁着美国旱地河流、水资源和生态系统的变化，而这些变化在传统上是难以预见的。对这些资源的可持续、适应性管理需要有能力预测它们将如何应对扰动。由于未来的驱动因素可能会远远超出过去观察到的条件，因此至关重要的是要有基于过程的模型，这些模型可以在历史可变性范围之外做出有用的，可转移的预测。然而，这种基于过程的模型的有效性只能通过与过去和现在行为的良好约束案例研究进行比较来证明。我们建议创建一个独特的新数据库，将提供一个宝贵的机会，研究的原因和后果的河流改造在几年到几十年的时间尺度。新墨西哥州的里奥普尔科盆地是西南部研究得最好、最具活力的盆地之一，它为我们的分析提供了跳板。在过去的世纪里，Rio Puerco及其洪泛区在水文、泥沙产量和植被方面发生了重大变化。这些变化中的许多都与20世纪20年代引进的外来树种柽柳有关，以及随后在整个山谷网络中的传播。最近，破坏柽柳的努力导致了河道几何形状和沉积物产量的巨大变化。因此，Rio Puerco代表了一个独特的自然实验，研究长期植被变化对动态河流系统的影响。为了利用这个实验，我们建议建立和分析一个数据库，集成历史流量和泥沙数据，时间序列测量的通道横截面的形式，现代和历史的植被模式，洪水沉积模式，和高分辨率测量最近的通道变化来自激光雷达图像。我们的分析包括两个时间尺度：（1）事件尺度，解决了大洪水的影响与事件前后的激光雷达，（2）年代际尺度，重点是从20世纪30年代到现在的tamberk蔓延的反应。除了提供新的洞察河流改造，综合数据库将提供一个独特的平台，为科学界测试和完善下一代的耦合流-沉积物-植被models.Intellectual优点：旱地河流环境体现了丰富的反馈之间的洪水流量，河岸植被，通道几何形状，细泥沙侵蚀，水库淤积，在流渗透和水质。通过在广泛研究的测试案例中探索系统，本项目将阐明这些反馈的性质和幅度。该项目还将对下述假设进行第一次检验，即有可能根据基本原则计算出旱地河流系统在年度至数十年时间尺度上对水输入和植被覆盖扰动的反应。该项目将研究、教育、通过以下项目进行推广：（1）与K-12教师合作，将令人兴奋的河流动力学科学带入课堂，（2）本科生和研究生参与跨学科研究，（3）通过开发和分发研究包，包括水，沉积物和植被随时间变化趋势的数据分析练习，以及说明过程和反馈的模型动画，扩大推广范围。我们还解决了一个重要的社会需要预测的潜在后果的环境管理行动，如最近推出的tamerik叶甲虫作为生物防治剂。最后，我们将制作并分发一个详细的定量数据库，用于对未来模型进行基准测试，时间范围从单一洪水事件到八十年的河流改造。

Summary: The arid American West relies on rivers for much of its water. Pressures from population growth, climate change, and invasive plant species threaten to transform the nation's dryland rivers, their water resources, and their ecosystems in ways that have been traditionally difficult to foresee. Sustainable, adaptive management of these resources requires an ability to predict how they will respond to perturbations. Because future drivers are likely to reach well beyond the conditions that have been observed in the past, it is critical to have process-based models that can make useful, transferrable predictions beyond the historical range of variability. The validity of such process-based models can only be demonstrated, however, by comparison to well constrained case studies of past and present behavior. We propose to create a unique new database that will provide a valuable opportunity to study the causes and consequences of river transformation over time scales of years to decades. One of the best studied and most dynamic basins in the southwest, the Rio Puerco, New Mexico, provides the springboard for our analysis. Over the past century, the Rio Puerco and its floodplains have undergone major changes in hydrology, sediment yield, and vegetation. Many of these changes are linked with the introduction of the exotic tree species tamarix in the 1920s, and its subsequent spread throughout the valley network. More recently, efforts to destroy tamarix have led to dramatic changes in channel geometry and sediment yield. Thus, the Rio Puerco represents a unique natural experiment in the effects of long-term vegetation change on a dynamic fluvial system. To take advantage of this experiment, we propose to build and analyze a database that integrates historical flow and sediment data, time series measurements of channel cross-section form, modern and historic vegetation patterns, flood sedimentation patterns, and high-resolution measurement of recent channel change derived from lidar imagery. Our analysis encompasses two timescales: (1) the event scale, addressing the impact of a large flood with pre- and post-event lidar, and (2) the decadal scale, focusing on the response to tamarisk spread from 1930s to present. In addition to providing new insight into river transformation, the integrated database will provide the scientific community with a unique platform for testing and refining the next generation of coupled flow-sediment-vegetation models.Intellectual Merit: Dryland river environments embody a rich set of feedbacks among flood flow, riparian vegetation, channel geometry, fine-sediment erosion, reservoir siltation, in-stream infiltration, and water quality. By exploring the system in the context of an extensively studied test case, this project will illuminate the nature and magnitude of these feedbacks. The project will also provide a first test of the hypothesis that it is possible to compute, from basic principles, the response of a dryland river system to perturbations in water input and vegetation cover on annual to multi-decadal time scales.Broader Impacts: The project closely integrates research, education, and outreach through a program of (1) partnership with K-12 teachers in bringing the exciting science of river dynamics into the classroom, (2) involvement of undergraduate and graduate students in interdisciplinary research, and (3) broader outreach through development, and distribution of study packages that include data analysis exercises in water, sediment, and vegetation trends over time, and model animations that illustrate processes and feedbacks. We also address an important societal need to predict potential consequences of environmental management actions, such as the recent introduction of tamarisk leaf beetle as a biocontrol agent. Finally, we will produce and distribute a detailed, quantitative database for benchmarking future models, on time scales ranging from a single flood event to eight decades of river transformation.